Lab Balance and Scales – Our Guide

Analytical Lab Balances and Scales

A Lab Balance, or Lab Scale is the heart of any modern laboratory. For many laboratories this piece of equipment is the most accurate and precise instrument in the laboratory. Able even to weigh finger prints on a glass beaker. All precise scientific measurements begin with a determination of the initial weight of a sample prior to any type of preparation procedure and subsequent analysis by the many high tech systems of separation and detection. Without an accurate, precise, and reliable measurement from the start, any following analytical procedure is negatively impacted and cannot be corrected. Accurate and reliable weighings are an absolute necessity in today’s laboratories and this should never be compromised. Today’s modern lab balances and scales are a true marvel of the advances in science and technology with barely any moving parts present. With this is mind it will be beneficial to go through a few of the features and technologies you will want to look for in any good lab balance or scale.

mettler ae200 lab balance Lab Balance and Scales Our Guide


How Accurate a Lab Balance or Scale Will You Need

This is really an easy question to answer. Of the many analytical lab balances and scales made today, you typically have a choice of either a four decimal place or a five decimal place balance. To put it more clearly, a four decimal place balance will be able to detect and measure 0.0001g (or 0.1 mg) and a five decimal place balance will be able to detect and measure 0.00001g (or 0.01 mg). It is certainly more difficult to measure 0.01 mg than it is to measure 0.1 mg. These small amounts on a balance are subject to any movement in the laboratory, any stray air current, temperature fluctuation or out of level table the balance may be sitting on. Detection and measurement in the 0.01mg range will be less stable than the reading in the 0.1 mg range, so if you don’t need this level of accuracy stick with the four decimal place balance. It will not tend to exhibit the instability seen in a measurement down to the 0.01 mg range.

A five decimal place lab balance or scale is only needed if you intend to weigh samples as small as 20 mg and below. For example, if you weighed a 20 mg sample (or 0.02000 g) on a five decimal place balance capable of measuring 0.00001g you would get an accuracy of 0.05% (0.00001/0.020000 × 100 = 0.05%).

Whereas, if you measure the same 20 mg sample on a four decimal place balance capable of measuring 0.0001g you would get an accuracy of 0.5% (0.0001g / 0.0200g ×100 = 0.5%). You would have a loss in accuracy by a factor of 10. Now these figures of 0.05% compared to 0.5% may seem small and insignificant but they are not in the world of analytical laboratories.

The degree of accuracy needs to be established before you pick and purchase a lab balance or scale. A five decimal place balance is more difficult to work with and typically has a smaller overall range. A four decimal place balance is much easier to work with and is not subject to all the room variables like temperatures, motions and vibrations (even from people just walking around the lab).

An easy solution to the above example is to increase your initial sample size by a factor of 10. For example, instead of using a 20 mg sample size, use a 200 mg sample size. This way you can use the much more stable four place balance and still have a sample accuracy of 0.05% ( 0.0001g /0.2000g × 100 = 0.05%). And then if you have the luxury, your subsequent sample preparation procedure could perhaps dilute by a factor of 10 to result in the same analytical solution if you would have started with a 20 mg sample. If you are not able to do this with your current method then you would have no choice but to use a five decimal place lab balance or scale.

One of the best options is to buy a balance capable of operating in two modes. Easily switchable between a four decimal readout or a five decimal readout. These are really the most versatile and well worth the additional cost if it is in your budget.

Six place lab balances and scales are also being used in some laboratories these days. These are very difficult to get a stable reading, sensitive to even the slightest movements throughout a building complex. These are used in those rare cases where sample size is very limited.

Lab Balances and Scales – Features and Highlights

Stray motions due to temperature changes, air currents, ambient noise, and the normal traffic of lab personnel have to be isolated from the lab balance or scale. Two absolute must haves for any good analytical lab balance is a built in glass enclosure isolating the weighing plate and a very heavy duty stable table. The table needed is a separate purchase and will not be covered in this article. All good analytical balances must come with a built-in four sided enclosure that isolates the sample and weighing pan. With this in mind, below are the most common features to look for.

  • Large easy to read digital LCD display.
  • Glass enclosure with easy access doors on at least two sides. In some cases three sides – the right, left and top.
  • An easy to access and read leveling bubble.
  • Easy to clean removable doors.
  • Built-in internal calibration weights.
  • Large easy to read and use access keypad.
  • Multiple weighing modes – with instant conversions to multiple units of weights.
  • ISO and GLP compliant printouts. A must for many industries today.
  • Easy to use adjustable leveling feet.
  • Can be connected to a printer.

Lab Balances and Scales – Conclusions

The lab balance-scale is the foundation of any good analytical laboratory. The quality of the lab balance will in many cases dictate the overall quality of the laboratory. Just as an outstanding member of any team can raise the performance of all the members, the lab balance becomes the pivot point from which all results derive. The cost of a good laboratory balance is small compared to the performance and durability of these marvels. Some of the top manufactures of quality lab balances – like Mettler-Toledo, Sartorius, and Ohaus to name a few – have produced some remarkable instruments for today’s modern laboratories.

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